Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the human central nervous system (CNS) that affects patients with impaired immune systems, including AIDS. A human papovavirus, JC virus, (JCV), has been implicated as the etiologic agent of this disease. JCV infects over 70 percent of the population at a very young age with no apparent clinical symptoms. In the brain of PML patients, viral particles are detected in cells of glial origin, i.e. oligodendrocytes and astrocytes. These cells are destroyed or transformed upon reactivation of the latent virus, resulting in demyelinating lesions in the brain. Reactivation of the virus and appearance of disease is associated with severe immunosuppression of cell- mediated immunity, yet the nature of control exerted by the immune system and mechanism that maintains JCV in its latent state is not understood. Results from a series of molecular and cellular studies revealed the involvement of several signaling pathways transmitted by immune cells via cytokines and immunomodulators that control expression and replication of the viral genome. In order to understand the underlying mechanism that controls replication of this neurotropic virus in glial cells, we have developed an in vitro cell culture system which allows us to investigate JCV DNA replication in the presence of immune cell secretory factors. Our results indicate that supernatant derived from activated immune cells is capable of suppressing replication of viral DNA in glial cells. Results from in vitro DNA-binding studies indicate that treatment of glial cells with T cell supernatant leads to elevated levels of nuclear protein in glial cells which binds specifically to the origin of viral DNA replication. Thus, we hypothesize that signals transmitted by functional immune cells to glial cells induce expression/activity of a suppressor protein which, by binding directly to the viral DNA sequence or indirectly via interaction with other regulatory proteins, prevents replication of the virus in these cells. In the absence of functional immune cells (i.e. immunosuppression), the lack of this barrier in glial cells permits viral replication in glial cells and the development of clinical disease in braom. To examine our hypothesis we propose to use immune cells from normal as well as immunosuppressed patients with PML to decipher the cross- communication between immune and nervous system and JCV gene expression. Furthermore, by employing nucleic acid array technology, we should gain important information on determining the portrait of cytokines and immunomodulators in healthy and diseased immune cells, as well as in glial cells exposed to immune cell factors from normal, and PML patients. The results of these experiments will provide unique information regarding the mechanisms involved in the reactivation of JCV in immunosuppressed individuals, and provide us with an intriguing biological tool to develop and use an antibody against the signaling factor/suppressor protein to determine its level in PML brain biopsy and normal brain tissue by immunohistochemical analysis, and to devise a strategy to block replication of the JCV genome.